Braking mechanism



March 1 1927.

A. H. G. GIRLING BRAKING MECHANISM Filed Aug. 18, 1926 2 Sheets-Sheet 1 Yaw I r I I A. H. G. GIRLING BRAKING MECHANISM March 1 1927. 1,619,718

Fil ed Aug. 18, 1926 2 She ts-Sheet 2 M, $232 airman Patented Mar. 1, 1927.

ALBERT HENRY GODFREY GIRLING, 0F HARLOW, ENGLAND.

BRAKING MECHANISM.

Application filed August 1a, 1926, Serial No.

This invention relates to expanding brakes of the type-wherein two brake levers, associated each with a brake shoe, are arranged to be moved apart by an expanding member so as to force the shoes against a rotary member, such as a drum, to be braked. In such brakes the levers are usually mounted on separate fixed pivots or on one fixed pivot common to them both, and the frictional faces have heretofore usuall formed a part of or been rigidly secure to the levers. This known arrangement has various defects, such as uneven wear owing to unequal distribution of pressure over the frictional faces, which in turn reduces the effective area of the frictional faces.

This invention has for one of its objects to increase the area of frictional face which shall be in'use and thereby to increase the life of the brake. equalize the distribution of pressure over as large an area of the brake drum as possible and thereby reduce stresses tending to distort the drum. A further object is to increasethe powerof brakes of the type described, without increasing their size. A still further object is to im rove the clearance conditions between the rake shoes and the drum when the brake is not in use. Still another object is to provide that a greater proportion of the bulk of the frictional liners can be worn away than heretofore, whereby the life of the brake is increased.

According to the invention there is provided in an expanding brake of the character described, the combination with a lever mounted to rock towards and away from a member to be braked, and means for rocking the lever, of brake shoes so pivotally mounted one behind another on said lever as'to co-o erate in tandem with the member to be raked.

Other features of the invention will be described hereinafter and pointed out in the claims.

Several embodiments of the invention are diagrammatically illustrated by way of example in the accompanying drawings, Wherein- Figure 1 is a side elevation showin an expanding brake of the type describe according to the invention, the brake shoes on one brake lever being arranged difierently, however, from those on the other, and

Figure 2 is a vertical section taken on the line 22 in Figure 1;

Another object is to- 129,950, and in Great Britain May 12, 1925.

Figures 3 and 4 are like views respectively of a modified construction of brake according to the invention, part of the device having been removed in Figure 3;

Figure 5 is a diagram referred to hereinafter; I

Figure 6 is a side elevation of a single brake lever carrying shoes according to another form of the inventiomand Figures 7 and 8 are cross-sections taken respectively on the lines 77 and 88 in Figure 6.

Like reference numerals designate corresponding parts throughout the several views. I

Referring to Figures 1 and 2, the brake levers 20, 21 inside a rotary drum 22 are mounted to rock at one end, as about a fixed Pivot-pin 23 which is preferably common to them both. A cam expander 24 cooperates with the other ends of the levers in the known manner for applying the brake, two springs 25 en aging both levers being provided as usual for contracting the brake. V

The brake levers 20, 21 carry each a pair of brake shoes 30, "30, 31 and 31, respectively, by means of pivot-pins 32 that pass through bosses in the webs of the shoes and through the levers. As clearly shown in Figure 2, the shoes 30 and 30 are of U sec-' tion this being a simple and inexpensive construction, whilst the shoes 31 and 31 are split in the direction of their length and comprise two parallelside parts held together by fastening strips 33, the pivotins 32 on which they are mounted being integral with the lever 21. This arrangement is useful where there is only a small space available for a lever of deep/section, in which case to perforate the lever would unduly weaken it. The shoes 30 and 30 can rock about their pivots independently of one another, but the shoes 31 and 31" have their adjacent ends so operatively connected as to cause them to rock in unison. As illustrated, the shoe 31 has a recess 34: in the form of an open-ended slot extendin in the direction of length of the shoe, an the shoe 31 has a rounded lug 35 extending into the recess. It is to be understood that each lever 20,21 may have the same construction and arrangement of shoes as the other if desired.

It will be observed that the .frictionalface of each shoe extends over about 90 of are,

and that their axes of pivoting lie on radii of the brake drum which are about 90 apart, so that .the four shoes in one drum have a total frictional face nearly equal in length to the inner periphery of the drum. In this way a maximum area of frictional contact is obtained, ap roximately e ual radial movement of the s oes is obtaine at four ints of the circumference of the interna periphery of the drum (i. e. at the said radii on which the pivots 32 lie) and owin to pivotally mounting the shoes substant1a1ly equal distribution of pressure over their whole area is ensured.

To prevent noise from developing due to wear of the parts or chatter between the shoes and the drum, frictional devices in the formof anti-rattling devices may be pro- In this construction of brake the two brake levers 40, 41 comprise each two arms lying side by side, between which the webs and bosses of the shoes 42, 42 and 42", are

held by pivot-pins 43 that pass through the j bosses. In Figure 3 one arm of the lever 41 is shown removed for the sake of clearness. Springs 44 which engage in slots in the webs of the shoes 42" and 42", and at the underside of bosses on the lever arm serve to take up any backlash at the pivots and to prevent rattling by imposing a slight frictional restraint on the rotation of the shoes about their pivots. The shoes 42 and 42 ma be coupled together at their adiacent en 3 bya ball-and-socket joint (simi ar to that described in connection with Figure 1) so that they are compelled to rock in unison for the purpose of equalizing the distribution of pressure.

Figure 5vis a diagram illustrating how the brake power is, under usual conditions, increased by an amount up to 40% or, under special conditions, even more. In the ordinary'brake shoe 50 used heretofore, in which the frictional face is rigidly connected with the brake lever, the center of braking pressure lies in a line 0. The braking pressure which we may designate O, in proportion to the cam force e, is equal to v This will be apparent by taking moments about the fixed pivot point of the brake lever. In the case where m and n are equal,

the braking pressure equals 0 or 2 e.

As shown in Figure 5 m and n are equal to the distances from center of braking pressure to the I fixed pivot point of the brake lever and to the center of force a plied by the cam 24 respectively. In t e present arrangement, the braking pressure is alon the lines 8 and s Designating the brfiiing pressures as s, and 8, respectively, the total braking pressure exerted may be summarized as follows:

Inasmuch as m and n are equal and, the angle between the lines of application of the braking pressures and the line joining the pivot point 23 and the center of application of the cam force equals 45, m and 11. may both be set equal to 1, and p, to .7. There-' fore,

and 8 '+8 =2.8 e, namely 40% more than that developed by the ordinary brake shoe.

Figures 6, 7 and 8 show a brake shoe unit which can be applied to an existing brake of the type described. This unit comprises a brake lever 60 on which shoes 61, 62 are pivoted at 63 and 64, respectively. In order to prevent the shoes seizing on to their pivots 63,64 by reason of rust, small bronze bushes 65 and 66 are pressed into the shoes 61, 62, respectively. In order to keep the shoes firmly down-on to their pivots for preventing rattling and to take up slackness resulting from Wear on the bushes or pivots, springs 67 and 68 are provided bearing on the top of the bushes. These springs are deflected by a pin 69 passing through the lever at their centres in order to create the necessary stresses on the bushes. The static stresses exerted by the springs 67, 68 also create suflicient friction between therespective parts between the shoes and the lever 60 to prevent the former from moving quite freely in relation to the latter, thus preventing chatter between the shoes and the brake drum when the brake is off. The pivots 63, 64,are each revented from moving out of place endwlse by a small pin 70 that enters into an annular groove "in the pivot and is held in place by a screw 71carried by the shoe.

'VVhen the brake is commonly used in one direction of rotation the trailing ends of the shoes maybe the longer thanthe leading ends, as shown at the bottom of Figure 1,-

ment is due to the tangential force developed at the'frictional face and if not,coun-.

terbalanced would tend to cause unequal wear at the ends of the shoe. Since at the CJI adjacent ends of two shoes of equal length ivoted in the middle (Figure 6), the forces sue to this moment are equal in amount but opposite in direction it is only necessary to couple these ends together to negative the effect of the moment. In the construction shown in Figure 6 one end of the shoe 61 slidably bears on the adjacent end of the shoe 62.

As compared with brakes of the type .described known heretofore the improved constructions according to the' invention from the middle of the levers instead of at their centres, the mechanical advantage is increased and, consequently the power of the brakeis increased by about 40%.

(4) The clearance conditions between the shoes and drum when not in use are improved. In known brakes of the type described the clearance space -is a rigidly defined crescent-shaped area and, the frictional face being long, the clearances at the ends of the crescent are ver small. In the present brake the only rigld clearances lie along radii containing the shoe pivots, situated about 90 apart, and being much nearer the centre of the lever than the extreme ends ofknown liners the rigid clearance is greater. The clearances at the ends of the shoes according to this invention are variable because each shoe can rock about its pivot.

(5) A greater proportion of the bulk of the frictional liner can be worn away than member to be braked, and means for rocking the lever, of brake shoes so movably supported in tandem on said lever that when one end of either shoe moves away from its supporting lever and towards the member to be braked, the other end of the same shoe, respectively, can move towards its supporting lever and away from the member to be braked.

2. In an expanding brake. of the char acter described, the combination with alever mounted to rock towards and away from a member to be braked, and means for rocking the lever, of brake shoes so pivotally mounted in successive relationship on said lever as to co-operate in tandem with the member to be braked.

3. In an expanding brake of the character described, the combination with a lever mounted to rock towards and away from'a member to be braked, and means for rocking the lever, of brake shoes so pivotally mounted in successive relationship on said lever as to co-operate in tandem with the member to be braked, the adjacent ends of which shoes are so operatively connected together as to cause the shoes to rock in unison on their supporting lever.

4. In an expandin brake'of the character described, the combination with a lever mounted to rock towards and away from a member to be braked, and means for rocking the lever, of brake shoes so pivotally mounted in successive relationship on said lever as to co-operate in tandem with the member to be braked, the adjacent ends of ad acent shoes having respectively one a recess and the other a lug movable in the recess 5 In an expandin brake of the character described, the com ination with a lever mounted to rock towards and away from a member to be braked; and means for rock ing the lever, of brake shoes so pivotally mounted in successive relationship on said lever as to co-operate in tandem with the member. to be braked, the pivotal axis of each shoe being situated nearer one end of the same than the other.

6. In an expanding brake of the character described, the combination with a lever mounted to rock towards and away from a member to be braked, and means for rocking the lever, of brake shoes so pivotally mounted in successive relationship on said lever as to co-operate in tandem with the member to be braked, the trailing end of each shoe being longer than the leading end.

In an expanding brake of the character described, the combination with a lever mounted to rock towards and away from a member to be braked, and means-for rocking the lever, of brake shoes so pivotally mounted in successive relationship on said lever as to co-operate in tandem with the member to be braked, and anti-rattling means tending toprevent movement of the shoes in relation to the supporting lever.

. 8. In an expanding brake of the character described, the combination with a lever Ill mounted to rock towards and away from a member to be braked, and means for rocking the lever, of brake shoes so pivotally mounted in successive relationship on said lever as to co-operate in tandem with the member to be braked, and resilient means constituting an anti-rattling device tending to prevent the shoes from rocking about their pivotal axes.

9. In an expanding brake of the character described, the combination with a lever mounted to rock towards and away from a member to be braked, and means for rocking the lever, of two brake shoes so pivotally mounted in successive relationship on said lever as to co-operate in tandem with the member to be braked, and a spring common to both shoes tending to hold the Pivots of the shoes against rattling on the lever supporting them.

10. In an expanding brake of the character described, a combination with a brake lever of a plurality of transverse pivot pins on said lever between its ends, a plurality of brake shoes mounted to rock about said pivots and coact with a member to be braked, a plurality of bushes in the shoes adapted to receive the pivot pins, and springs carried by the lever and bearing upon the bushes.

11. In an expanding brake of the character described, a combination with a brake lever of a plurality of transverse pivot pins mounted to move endwise between said levers between its ends, a plurality of brake shoes of U section embracing said lever, and mounted between its ends on said pivot pins bushes in the shoes adapted to receive the pivot pins, a plurality of bearings carried by the lever and bearing on the bushes, and means for locking the pivot pins against longiti'ldinal'movement in said lever.

12. In an expanding brake of the character described, the combination with a brake lever, of a transverse pivot-pin mounted to move endwise in said lever between its ends, a brake shoe of U section embracing said lever and mounted between its ends on'said pivot-pin that extends at both ends into the sides of the shoe, two bushes in the shoe, each receiving one end ofthe pivot-pin, two springs carried by the lever and bearing each on one of said bushes, and means for locking said pivot-pin against endwise move- 'ment in said lever.

In testimony whereof I afiix my signature.

ALBERT HENRY GODFREY GIRLING. 

